Sequencing Batch Reactor Cycle Research Articles

A stochastic approach for the solution of single and multi–objective optimisation problems of biological processes in sequencing batch reactor

This paper investigates the impact of implementing single and multi-optimisation solutions on the biological treatment process in a sequencing batch reactor (SBR). The research is based on a case study of the water resource recovery facility (WRRF) in Swarzewo, Northern Poland. The paper introduces the adaptive extremum seeking control (ESC) method for dissolved oxygen (DO) concentration control and places it in a layered control structure. Further, it presents the introduction of an optimisation layer for the structure and parameters of the SBR cycle, through the synthesis of stochastic methods: single-objective optimisation (SOO) using a genetic algorithm (GA) and multi-objective optimisation (MOO) using the NSGA-II algorithm. The results were compared to a classical approach with fixed cycle parameters. The paper shows the advantages of optimising cycle parameters, including the number of phases as well as the DO value, on the process flow. These control structures underwent simulation tests in the MATLAB environment with the Simba package. The biochemical processes occurring in the reactor are based on the Activated Sludge Model No. 2d (ASM2d). The optimising control system demonstrates tangible improvements in operational efficiency and significant reductions in electrical energy consumption, highlighting the effectiveness of the proposed methodologies. © 2017 Elsevier Inc. All rights reserved.

Fast start-up of partial nitrification for high-ammonia wastewater treatment using zeolite with in-situ bioregeneration

Partial nitrification (PN) has been successfully applied in treating wastewater with medium or low concentrations of ammonia, whereas the treatment of high-concentration ammonia wastewater remains a great challenge due to the inhibition of ammonia-oxidizing bacteria (AOB) by excessive free ammonia (FA). In this study, the zeolite adsorption and bioregeneration synergy were utilized to enhance the PN of sequencing batch reactors (SBRs) for treating high-ammonia wastewater (500– 1000 mg NH4+-N/L). The SBRs with natural zeolite (N-Zeolite) and modified zeolite (M-zeolite) could successfully start-up within 8 days (90 % ammonia nitrogen removal (ANR) and 71 % nitrite accumulation rate (NAR) for SBR with N-Zeolite, and 81 % ANR and 84 % NAR for SBR with M-Zeolite), while the SBR without adding zeolite failed to start-up (40 % ANR). The PN enhancement may be attributed to the rapid adsorption of NH4+ by zeolite and the subsequent bioregeneration in an SBR cycle, which allowed a lower ammonia level in the bulk solution and alleviated the inhibition of FA on AOB, thus enabling a sustainable PN. Compared with M-zeolite, N-zeolite may be more practical for high-ammonia wastewater treatment owing to its fair performance, low cost, and simple maintenance. These results revealed that the “adsorption”-”saturation”-”desorption” process of zeolite was favored to construct a virtuous cycle of nitrification-pH-FA equilibrium in SBRs, which broadens the knowledge of biotransformation in high-ammonia wastewater and in-situ regeneration mechanism of zeolite and provides a highly efficient and practical method for treating high-ammonia wastewater.

Comparison of benzotriazole ultraviolet stabilizers (BUVs) removal from wastewater after subsequent stages of sequencing batch reactor (SBR) treatment process

The research focused on benzotriazole ultraviolet stabilizers (BUVs) which are commonly used compounds despite being found dangerous, e.g. promoting breast cancer cell proliferation, damaging vital organs such as hearts, brains livers and kidneys. The aim of the study was to analyse the efficiency and removal rate of BUVs from wastewater depending on the quantity of tested compounds and SBR anaerobic-aerobic conditions. The study was conducted in sequencing batch reactors (SBRs - 17 L) with real flocculent activated sludge (8 L) and model wastewater (5 L) containing UV-326, UV-327, UV-328, UV-329 and UV-P from 50 to 600 μg∙L−1. The SBR were operated in 390 cycles of 7 h and 10 min over 130 days. The similarity of the technological parameters of the treatment process to those used in a real wastewater treatment plant was maintained. Efficiency removal of individual BUVs was strictly dependent on the dose of compounds introduced into wastewater and ranged from 68.2 to 97 %. Removal of UV-329 occurred with lowest efficiency (from 68.2 to 85.2 %) while UV-326 was most efficiently removed from the wastewater (from 94.1 to 97 %). UV-329 was removed from wastewater with the lowest (0.0968–0.9524 μg∙L−1∙min−1) average removal rate while UV-327 with the highest (0.16–1.3357 μg∙L−1∙min−1), irrespective of BUVs dose in the influent. Secondary release of BUVs into the wastewater occurred in SBR during the settling phase and was dependent on the type and concentration of the BUVs in the raw wastewater. This occurrence was noted for UV-326 ≥ 100; UV-327 = 600; UV-328 ≥ 200; UV-329 ≥ 50 and UV-P ≥ 100 μg∙L−1. The settling phase needs to be shortened to the required minimum. This is an important conclusion for WWTPs in regards to SBR cycle duration and technological parameters of the treatment process.

Potential causes of partial-denitrification (PD) granular sludge breakdown under high nitrate loading rates

The granule instability has been frequently reported during the operation of high loading rates. While, there no research was performed on the recently developed anoxic partial-denitrification (PD) granules, a novel pathway in producing nitrite from nitrate for anammox process. Herein, this work, for the first time, investigated the influence of nitrate loading rates on the instability of PD granules and identified the key causes. Two lab-scale sequencing batch reactors (SBRs) were operated with nitrate loading rates (NLR) increased from 0.48 to 3.84 kg N/m3/d (R1, 8 cycles/d), and 0.96 to 7.68 kg N/m3/d (R2, 16 cycles/d) by gradually elevating the influent nitrate concentration. Results showed that nitrite production rates increased with the NLRs, with a maximal value of 5.26 kg N/m3/d obtained. However, the compact regular PD granules were not stable and broke down when NLR was above 3.84 kg N/m3/d, which resulted in serious sludge washing out from SBR. The high NLRs led to the extracellular polymeric substances (EPS) transformation in terms of its composition and structure, which the protein content in the EPS and the tightly bound EPS (T-EPS) fraction was significantly decreased, this was supposed to be the major reason causing the breakdown of PD granules. Besides, it was found the PD granule in R2 was more deteriorated than that in R1 under the same high NLR, suggesting the short starvation (idle) times in SBR cycle was likely another reason impairing the stability of PD granules. Overall, this research provides useful information in development of granule-based PD systems and sheds light on achieving high-rate nitrite production in SBR with great stability.

Evaluation of operating parameters affecting the two-stage nitritatin/anammox process in mainstream flows: From lab-scale to pilot-scale

Operating parameters for the two-stage nitritation/anammox (PN/A) process in mainstream flows from lab-scale to pilot-scale were investigated. In the batch experiment, the specific activities of ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) were fitted with a Monod model, and the oxygen affinity of NOB was higher than that of AOB. Nevertheless, dissolved oxygen concentrations higher than 2.0 mgO2/L were effectively applied for selective inhibition of NOB. In addition, organic matter was evaluated as the operating parameter that inhibited the activity of NOB more selectively than AOB under mainstream conditions. The operating parameters determined in the batch experiment were verified in a continuous experiment, and it was shown that the shortening of hydraulic retention time with increasing aeration time in the sequencing batch reactor cycle has the potential to selectively enhance the activity of AOB over NOB. The effect on the C/N ratio and temperature in a lab-scale anammox reactor was investigated. The denitrification with the addition of organic matter contributed to the improvement of nitrogen removal efficiency, but a C/N ratio of more than 1.0 severely deteriorated the sludge settleability. The operating factors for the mainstream PN/A determined in the lab scale were applied to the pilot plant. As a result, a nitrogen removal efficiency of 79 ± 11% was stably achieved with effluent total nitrogen of 2.6 ± 1.5mg/L. However, unpredictable fluctuations in environmental factors revealed that residual ammonium was another critical factor affecting mainstream PN/A.

Elemental distribution of latex‐based aerobic granules and its effects on micromorphological properties and settling performance

AbstractThis study focuses on the settling profile and chemical characteristics of latex aerobic granules cultivated from rubber industrial wastewater. Latex‐based aerobic granular sludge (AGS) was cultivated using sequencing batch reactor (SBR) in supplemented with synthetic wastewater (SW) as nutrients feeding for biogranulation process. The bioreactor was operated for 24 h with eight series of intermittent 3 h SBR cycles continuously. The SBR configuration comprises of five operation phases from SW feeding, aeration, settling, and effluent decanting to idle. Latex granules exhibit a loose and irregular structure dominated by coccal‐shaped bacteria with an average size of 4.0–5.0 mm and a settling velocity of 0.35–0.53 m h–1. The elemental analysis using X‐ray fluorescence (XRF) showed that the latex granules contained various elements while X‐Ray diffraction (XRD) analysis suggested the presence of zincowoodwardite, berlinite, rutile, and quartz. Fourier transform infrared spectroscopy (FTIR) analysis revealed the presence of aliphatic hydrocarbons, alkene, alkyne, and tertiary amine.

Effect of the organic loading rate on the PHA-storing microbiome in sequencing batch reactors operated with uncoupled carbon and nitrogen feeding

Over the last years, in a search for sustainable and biodegradable alternatives to petrol-based plastics, biotechnological applications turned to the potentialities of mixed microbial cultures (MMC) for producing polyhydroxyalkanoates (PHAs). Under a feast and famine regime, an uncoupled carbon (C) and nitrogen (N)-feeding strategy may be adopted by dosing the C-source at the beginning of the feast and the N-source at the beginning of the famine in order to stimulate a PHA storage response and microbial growth. Even though this strategy has been already successfully applied for the PHA production, very few information is to date available regarding the MMC operating in these systems and the influence of Organic Loading Rate (OLR) on their selection and enrichment. To fill the gap, this study investigated the effect of the OLR on the selection of PHA-accumulating microorganisms in a sequencing batch reactor (SBR) operated with an uncoupled C and N feeding strategy. The SBR cycle length was set at 12 h and four OLRs values (4.25, 8.50, 12.75 and 18 gCOD L−1 d−1) were tested by changing the concentration of the feeding solution, made of a synthetic mixture of acetic (85% of the overall COD) and propionic (15%) acids. The PHA-storage yield increased by increasing the OLR (up to 0.69 COD/COD at 12.75 gCOD L−1 d−1) but significantly decreased (0.27 COD/COD) at 18 gCOD L−1 d−1 concomitantly with a longer feast phase and a lower PHA content in the biomass at the end of the feast phase. The selective pressure induced by the applied OLRs strongly influenced the microbiome composition revealing a high content of putative PHA-storing bacteria, such as Rhodobacter, Thauera and Paracoccus, in the SBR operated at OLRs 4.25, 8.50 and 12.75 g COD L−1 d−1 (up to 97.4% of total reads) and a low content (5.4%) in the SBR at 18 g COD L−1 d−1where the predominance of genus Nitrinicola was instead observed.

Biodegradation of natural and synthetic endocrine-disrupting chemicals by aerobic granular sludge reactor: Evaluating estrogenic activity and estrogens fate.

In this study, the biodegradation of endocrine-disrupting chemicals (EDCs) (namely the natural and synthetic estrogens 17β-estradiol (E2) and 17α-ethinylestradiol (EE2), respectively) was assessed in an aerobic granular sludge (AGS) sequencing batch reactor (SBR) treating simulated domestic sewage. To better understand the fate of these compounds, their concentrations were determined in both liquid and solid (biomass) samples. Throughout the operation of the reactor, subjected to alternating anaerobic and aerated conditions, the removal of the hormones, both present in the influent at a concentration of 20μgL-1, amounted to 99% (for E2) and 93% (for EE2), with the latter showing higher resistance to biodegradation. Through yeast estrogen screen assays, an average moderate residual estrogenic activity (0.09μgL-1 EQ-E2) was found in the samples analysed. E2 and EE2 profiles over the SBR cycle suggest a rapid initial adsorption of these compounds on the granular biomass occurring anaerobically, followed by biodegradation under aeration. A possible sequence of steps for the removal of the micropollutants, including the key microbial players, was proposed. Besides the good capability of the AGS on EDCs removal, the results revealed high removal efficiencies (>90%) of COD, ammonium and phosphate. Most of the incoming organics (>80%) were consumed under anaerobic conditions, when phosphate was released (75.2 mgP L-1). Nitrification and phosphate uptake took place along the aeration phase, with effluent ammonium and phosphate levels around 2mgL-1. Although nitrite accumulation took place over the cycle, nitrate consisted of the main oxidized nitrogen form in the effluent. The specific ammonium and phosphate uptake rates attained in the SBR were found to be 3.3 mgNH4+-N gVSS-1.h-1 and 6.7 mgPO43--P gVSS-1 h-1, respectively, while the specific denitrification rate corresponded to 1.0 mgNOx--N gVSS-1 h-1.

Effect of sludge age on aerobic granular sludge: Addressing nutrient removal performance and biomass stability

The effect of the sludge retention time (SRT) on the stability and performance of an aerobic granular sludge (AGS) sequencing-batch reactor (SBR) on the simultaneous organic matter, nitrogen and phosphorus removal from simulated domestic wastewater was assessed in a long-term study (392 days). Operated under alternating anaerobic-aerobic conditions, the reactor was subjected to four experimental conditions: uncontrolled SRT (run I), SRT of 30 (run II), 20 (run III) and 15 days (run IV). The results showed that COD removal was kept stable and over 90 % throughout the SBR operation, regardless of the SRT. On the other hand, by allowing the sludge age to be dependent on natural solids washout by effluent withdrawal (SRT of 47–61 days), phosphate removal was substantially low (15 %), as also observed at an SRT of 30 days. Filamentous bacteria overgrowth was noticed at the later conditions, which affected the stability of the granular biomass, leading to a deterioration of its settling properties. The ratio between the sludge volume index after 30 and 5 min of settling (SVI30/SVI5) was around 0.70. Biological phosphate removal started to thrive at the sludge age of 20 days (35 %), reaching around 100 % at SRT of 15 days, at which the highest P-release/COD uptake ratio (0.14 mg P/mgCOD) and specific phosphate uptake (11.4 mgPO43−-P/(gVSS h)) were observed. Under the lowest SRT applied, the granules exhibited better structural and settling properties, with the SVI30/SVI5 ratio reaching almost 1.0. Moreover, nitrification was kept stable, and, even though nitrite build-up occurred during the SBR cycle, nitrate was the main oxidized nitrogen form in the effluent. Average COD, ammonium and total nitrogen removal amounted to 93 %, 97 % and 58 %. Cycle tests under normal and special conditions were carried out to assess specific nitrification, denitrification and phosphate uptake rates, and elucidate the key players in the biological conversions processes taking place in the AGS reactor. No phosphate uptake coupled to nitrate reduction was noticed, implying that P removal was not driven by denitrifying dephosphatation activity. To track the dynamics of important microbial functional groups, fluorescence in situ hybridization analysis was conducted.

Prediction of Paper Mill Wastewater Treatment Process Parameters in Sequencing Batch Reactor using Fuzzy Logic Technique

Integrated paper and pulp mills utilize logs and wood chips for the production of paper. During the process, the expose of raw effluents affect the environmental factors. In this analysis, waste water from paper mills was processed with the SBR (sequencing batch reactor) cycle. The effect of microbes and aeration periods with varying amounts of waste water on the efficiency of SBRs has been evaluated. During the tests, removal efficiencies of COD, BOD and TDS have been tracked. For experimental design, study and optimization, Box-Behnken core composite architecture was implemented. To maximize SBR performance, Fuzzy logic control was used. The SBR demonstrated higher efficiency in removal output on the basis of the tests. At the optimum conditions of microbe dosage of 55 ml aeration time of 5 hrs and wastewater concentration of 75% and the SBR achieved maximum removal percentage of COD, BOD and TDSis 88.18%, 91.80% and 87.12%respectively.

Optimization of nitrogen removal performance in a single-stage SBR based on partial nitritation and ANAMMOX

A partial nitritation (PN)/anaerobic ammonium oxidation (ANAMMOX) process in sequencing batch reactor (SBR) was successfully developed to treat high-strength ammonium wastewater. The feed distribution in the SBR cycle and sub-cycles was considered as the main operating strategy, and was optimized using a response surface methodology (RSM)-based optimization technique. In the SBR cycle, the maximum nitrogen removal rate (NRR) of 0.79 ± 0.01 kg m−3 d−1 was achieved by applying a feed distribution strategy that considered the kinetic characteristics of ANAMMOX and ammonia oxidizing bacteria (AOB). However, this strategy negatively affected the nitrogen removal efficiency (NRE) due to alkalinity loss. Therefore, the feed distribution in the SBR sub-cycles with respect to the NRE and the NRR was further studied. The nitrogen removal performance was optimized in the optimum region and an NRE of 88% and an NRR of 0.84 kg m−3 d−1 were achieved. The optimized model was verified in confirmation test. The RSM-based optimization results provide insights into the feed distribution strategy for achieving single-stage PN/ANAMMOX SBR operation.

Effects of carbon source on the formation, stability, bioactivity and biodiversity of the aerobic granule sludge

Three aerobic granular sludge systems were operated as sequencing batch reactors (SBR) with acetate, ethanol and glucose as carbon source. The SBR cycle was 6 h, with an anaerobic phase followed by an aerobic phase. The acetate granules (>1.5 mm) had the greatest microbial diversity and better results in terms of removal efficiency for carbon and nutrients (TN ≈ 72% and TP ≈ 42%) and also in the resistance tests. However, partial disintegration was observed. On the other hand, when ethanol was the substrate, the granules were stable, good nitrogen removal was achieved (TN ≈ 53%), but phosphorus removal was not favored (TP ≈ 31%). Glucose presented the lowest efficiency values for nitrogen (TN ≈ 44%) and phosphorous removal (TP ≈ 21%), and the granules formed (<1 mm) had the lowest microbial diversity. Therefore, the carbon source had a high impact on the characteristics of the granules.

Nitrifiers activity and community characteristics under stress conditions in partial nitrification systems treating ammonium-rich wastewater

Long-term exposure of nitrifiers to high concentrations of free ammonia (FA) and free nitrous acid (FNA) may affect nitrifiers activity and nitrous oxide (N2O) emission. Two sequencing batch reactors (SBRs) were operated at influent ammonium nitrogen (NH4-N) concentrations of 800mg/L (SBRH) and 335mg/L (SBRL), respectively. The NH4-N removal rates in SBRH and SBRL were around 2.4 and 1.0g/L/day with the nitritation efficiencies of 99.3% and 95.7%, respectively. In the simulated SBR cycle, the N2O emission factors were 1.61% in SBRH and 2.30% in SBRL. N2O emission was affected slightly by FA with the emission factor of 0.22%–0.65%, while N2O emission increased with increasing FNA concentrations with the emission factor of 0.22%–0.96%. The dominant ammonia oxidizing bacteria (AOB) were Nitrosomonas spp. in both reactors, and their relative proportions were 38.89% in SBRH and 13.36% in SBRL. Within the AOB genus, a species (i.e., operational taxonomic unit [OTU] 76) that was phylogenetically identical to Nitrosomonas europaea accounted for 99.07% and 82.04% in SBRH and SBRL, respectively. Additionally, OTU 215, which was related to Nitrosomonas stercoris, accounted for 16.77% of the AOB in SBRL.

Simultaneous pyridine biodegradation and nitrogen removal in an aerobic granular system

Simultaneous pyridine biodegradation and nitrogen removal were successfully achieved in a sequencing batch reactor (SBR) based on aerobic granules. In a typical SBR cycle, nitritation occurred obviously after the majority of pyridine was removed, while denitrification occurred at early stage of the cycle when oxygen consumption was aggravated. The effect of several key operation parameters, i.e., air flow rate, influent NH4+-N concentration, influent pH and pyridine concentration, on nitritation, pyridine degradation and total nitrogen (TN) removal, was systematically investigated. The results indicated that high air flow rate had a positive effect on both pyridine degradation and nitritation but a negative impact of overhigh air flow rate. With the increase of NH4+ dosage, both nitritation and TN removal could be severely inhibited. Slightly alkaline condition, i.e., pH7.0–8.0, was beneficial for both pyridine degradation and nitritation. High pyridine dosage often resulted in the delay of both pyridine degradation and nitritation. Besides, extracellular polymeric substances production was affected by air flow rate, NH4+ dosage, pyridine dosage and pH. In addition, high-throughput sequencing analysis demonstrated that Bdellovibrio and Paracoccus were the dominant species in the aerobic granulation system. Coexistence of pyridine degrader, nitrification related species, denitrification related species, polymeric substances producer and self-aggregation related species was also confirmed by high-throughput sequencing.

On-line estimation of the aerobic phase length for partial nitrification processes in SBR based on features extraction and SVM classification

We present a strategy for the on-line estimation of the aerobic reaction phase length for a partial nitrification process with pH and dissolved oxygen closed-loop control. To overcome existing drawbacks associated to partial nitrification (e.g., non-linearities and time-variant behaviors), our strategy is based on feature extraction over manipulated variables to identify interesting patterns associated to the end-point of nitrification. We use a support vector machine (SVM) classifier as a decision tool to determine the end-point of the aerobic phase. A database of lab-scale sequencing batch reactor (SBR) cycles selected from ten months of operation was used to train and test the proposed decision-making strategy. Results for all 533 SBR cycles showed 100% correct classifications. Most aerobic phase lengths in the analyzed database had a reduction time around 20min, although time reductions greater than 60min were also achieved.

Real-Time Control System Based on the Values of Derivative of the Redox Potential Aiming Nitrogen Removal in a Sequencing Batch Reactor Applied in Treating Dairy Wastewater

This paper presents a real-time control strategy based on the derivative of the oxi-reduction potential (ORP) values for nitrogen removal via nitrite in a sequencing batch reactor (SBR) fed with effluent from an anaerobic sequencing batch reactor (ASBR) treating dairy wastewater. The developed control strategy optimized the length of aerobic and anoxic phases without external carbon source addition. Firstly, a fixed interval length for aeration period was used in the SBR cycle to promote the nitrogen removal; however, this strategy did not allow the proper alternation of anoxic and aerobic conditions, and thus effective removal of nitrogen was not verified. After that, the real-time control strategy was implemented, and the end of nitrification and denitrification processes was determined when the derivative of the oxi-reduction potential (ORP) was close to zero. This strategy provided a removal of 92.2 ± 9.7 and 63.9 ± 19.0% for concentrations of TKN-N and Nt-N, respectively, which were well above those found for the open-loop system—43.8 ± 21.6 and 26.5 ± 26.2% for the removal of TKN-N and Nt-N, respectively.

High-performance system for partial nitritation of reject water resistant to temperature fluctuation

A sequencing batch reactor (SBR) applying partial nitritation for reject water treatment was operated for 330 days at a laboratory scale. The system was repeatedly exposed to sudden temperature drops from 24 to 17 °C. The nitrogen loading rate (NLR) was increased incrementally from 0.4 to 1.5 kg/(m3 day) with the aim to evaluate temperature stability of the process at different NLR value. Total nitrite nitrogen (TNIIIN) represented 94–99% of oxidised nitrogen in the effluent throughout the entire operation of the reactor. It was found that the pH profile during the SBR cycle, nitrogen removal efficiency and concentration of N-species in the effluent did not show significant changes following temperature decreases occurring within the entire applied range of the NLR. Simultaneously, the nitrogen removal rate increased proportionally with the NLR where the nitrogen oxidation efficiency reached 48–58% regardless of actual temperature and NLR. These observations clearly demonstrate the temperature stability of applied partial nitritation system during the tested temperature fluctuations.

Enhancing a multi-stage process for olive oil mill wastewater valorization towards polyhydroxyalkanoates and biogas production

Olive oil mill wastewaters (OMW) cause serious environmental pollution problems due to their high level of production and specific chemical characteristics. An innovative disposal treatment and simultaneous valorization technology consists of using OMW as a no-cost substrate for mixed microbial culture (MMC)-based polyhydroxyalkanoates (PHAs) production process. Here, an MMC multi-stage process was developed in which after acidogenic fermentation, OMW was subjected to a solid liquid separation step by centrifugation. The resulting solid fraction was converted into methane through anaerobic digestion in order to recover energy for the process, whereas the liquid fraction was used as feedstock for both the biomass selection and the PHA accumulation step.Most of OMW soluble chemical oxygen demand (COD) content in the liquid fraction (approximately 70%) was removed in a sequencing batch reactor (SBR) obtaining a high PHA production (about 532mgCOD, in the feast phase). In particular, the strategy to uncouple COD feed from nitrogen supply within the SBR cycle, along with the operation of a settling phase before the famine phase, allowed to enhance the selective pressure towards PHA-storing microorganisms. Polymer production significantly increased in the accumulation reactor up to approximately 2470mgCOD/L. Finally, anaerobic digestion tests on the OMW solid fraction showed a relevant COD conversion into methane (up to 100%).

Online Monitoring of a Sequencing Batch Reactor Treating Domestic Wastewater

Domestic wastewater consists of considerable concentrations of pollutants that can boost water eutrophication if not treated before final discharge, which could damage the ecosystem and negatively affect human health. Sequencing batch reactor (SBR) technology is considered a promising biological wastewater treatment technology to address these issues. In recent years, SBR selection has increased as an effective technology for the treatment of domestic and industrial wastewaters due to its setup simplicity and ease of operation. However, many researchers have reported differences in cycle time. The importance and originality of this study is that it explores the parameters of pH, temperature, oxidation-reduction potential (ORP) and dissolved oxygen (DO) throughout the SBR cycle to predict the end of the treatment cycle. A laboratory-scale SBR was used in this study with a five-litre working volume. It was equipped with four electronic sensors (probes) to monitor the pH, ORP, temperature and DO. The SBR was operated under constant aeration, 1.0 l/min, ±12 C° temperature and 6h cycle time. Each cycle of the SBR operation included Fill (30minutes), React (240minutes), Settle (30minutes), Draw (30minutes) and Idle (30minutes). Influent and effluent samples were analysed for COD, ammonia-N and nitrate-N. The pH, ORP and DO values at the end of the 6h HRT treatment cycle were between 6.6-7.9, 147-169mV and 4.6-6.6mg/l respectively. The results show complete degradation of COD and nitrogen compounds was seen when the DO profile increased due to bacterial respiration. The results prove that online monitoring of SBR operating parameters could significantly predict the end of the treatment cycle, and the pH, DO and ORP profiles could be used as onsite process control parameters.

Respirometric response and microbial succession of nitrifying sludge to m-cresol pulses in a sequencing batch reactor.

A nitrifying consortium was kinetically, stoichiometrically and molecularly characterized via the in situ pulse respirometric method and pyrosequencing analysis before and after the addition of m-cresol (25mgCL-1) in a sequencing batch reactor (SBR). Five important kinetic and stoichiometric parameters were determined: the maximum oxygen uptake rate, the maximum nitrification rate, the oxidation yield, the biomass growth yield, and the substrate affinity constant. An inhibitory effect was observed in the nitrification process with a recovery of this by up to eight SBR cycles after m-cresol was added to the system. However, full recovery of the nitrification process was not observed, as the maximum oxygen uptake rate was 25% lower than that of the previous operation without m-cresol addition. Furthermore, the pyrosequencing analyses of the nitrifying consortium after the addition of only two pulses of 25mgCL-1 m-cresol showed an important microbial community change represented by a decrease in the nitrifying populations and an increase in the populations degrading phenolic compounds.